I suppose some could argue that it's more realistic. But no, it really isn't. It might make you look slightly huskier but not as much as that. And certainly not for things like leather armor. Light armor is supposed to be light but that looks anything but. It might be a good idea for a mod for someone to go in and shrink a few of those vertices a little closer together.
Well, but to make you look bulkier, it would make sense to also make the area on shoulders, chest and arms bigger. But if you look at the pictures, the chest is hugged almost perfectly, and so are the arms. the biggest berth is given to hips and waist
I never really noticed this, actually, it certainly never bothered me that much, of course I'm not in the habit of closely comparing the armored and unarmored bodies.
To be fair, though, unless clothing is designed to be completely form fitting, it probably isn't going to completely reflect the shape of your unclothed body, now I don't really know much about the details of Medieval armor, but at least for plate mail type things, I could imagine that they could easily make your physique look different while wearing them, and while the joints of glass armor appear to be chain, the actual glass parts in Oblivion look pretty plate-like to me. On the other hand, for leather to be like this is less excusable. But still it never really bothered me, honestly, I'm more concerned about whether the armor designs look good than how well it fits my character's physique, as long as there aren't any clipping issues or seams visible between the armor and exposed skin, and it isn't obvious that there's no way my character's body could actually fit in the armor, and as for whether the designs look good or not, some do, and some don't.
Well, the fact that the armour and clothing do not correspond perfectly is only my way of saying that it looks bad for me. I do not know, but I do not really want my characters to look fat or out of proportion in one armour, while it is better in another. I see this as an inconsistency as well.